Do not use sand paper for the same reason as the brown "cookie" style Scotch bright disks. You want to avoid abrasives in the engine at all costs. A good scraper, not a razor blade will get 99% of it off. You can use a wire wheel or one of the disks I mentioned earlier to get the rest. There are chemicals that also will dissolve old gaskets and gasket cement, I don't
recommend them but they are available.
A good scraper has a nice clean 90* edge, not a sharp edge like a razor.

Ok, scraper it is. I will also see if I can get the wire wheels too. I have used the spray-type gasket removers before but I would hate to get that stuff inside any ports or holes, etc.